A. Technical Field
The present invention relates generally to air-conduction hearing evaluation, and more particularly, to portable hand-held hearing testing and hearing aid fitting.
B. Description of the Prior Art
Air-conduction hearing evaluation involves the presentation of airborne sounds (test stimuli) to the ears of a test subject. The evaluation may involve threshold measurements whereby the threshold of hearing is determined at various frequencies, or suprathreshold measurements whereby loudness perceptions above threshold are determined. Suprathreshold testing include most comfortable loudness (MCL), uncomfortable loudness (UCL) and dynamic range measurements. A variety of test stimuli types are employed in audiological testing including pure tones, speech, and a variety of noise-based signals.
Test stimuli in air-conduction testing are emitted from a speaker to travel in air and ultimately reaching the eardrum. A speaker is typically positioned directly on or within the ear as in the case of circumaural earphones (headphones) and insert earphones. Alternatively, in sound field testing, a speaker is placed at a distance from the ear of the test subject in a test room (See American National Standard, specification for Audiometry, ANSI S3.6-1996).
Sound field evaluation generally involves bulky instrumentation, complex calibration procedures and require specialized test rooms. Furthermore, precise positioning of the subject with respect to a speaker is necessary in order to minimize errors in the intensity level of the sound at the ear. These errors are also caused by reverberations commonly found in test rooms (see Sandlin, R, Handbook of Hearing and Amplification, Ch. 6. pp 147–164, Singular Publishing group, 1995). FIGS. 6–3 of Sandlin, for example, demonstrate how large the variability of pure tone sound field measurement can be for small changes in distance between the subject and the speaker.
In standard sound field audiometry, the subject is typically placed approximately at 1 meter (m) from the speaker. Unfortunately, the reverberant component of sound at 1 millimeter (mm) is significant as shown in FIGS. 6–2 of Sandlin. The use of anechoic test rooms to eliminate reverberant sounds is extremely expensive and thus not employed in standard audiological test setups.
To minimize the effect of reverberant sounds, the subject should be positioned within the direct field of sound, which is typically within 70 centimeters (cm) from speaker. This causes the direct sound in the direct field to be dominant with respect to reverberant sound reflected from nearby objects in the room (i.e., walls, ceiling, floor, equipment, etc.). However, maintaining a precise seating arrangement within 70 cm of a speaker presents many challenges related to subject movement, discomfort, and even claustrophobia.
The utilization of probe tube microphone system to calibrate and regulate presentation levels has been widely used for various hearing evaluations (for example, see pp. 192–204 in Sandlin). However, probe tube microphone instrumentation requires careful positioning of the probe tube for each hearing evaluation step performed. Furthermore, the use of microphone probe tube systems adds considerable cost and complexity for the evaluation procedure, not to mention the inconvenience of attaching and maintaining a probe tube and its cabling for both the subject and the clinician.
In headphone audiometry (TDH-39 type for example), the distance between the test ear and the speaker is relatively stable thus alleviating the problem of speaker-subject positioning encountered in sound field audiometry. However, the headphone must be fitted in a sealing manner in order to minimize errors due to sound leakages that may occur at the headphone-ear contact area. Insert earphones (ER-3A type for example) also require a good sealing fit when inserted within the ear canal. Headphone and insert earphones can be uncomfortable and cumbersome for many individuals. Furthermore, headphone and insert earphones are particularly problematic for aided evaluation (with a hearing aid placed in the ear) because they generally interfere, physically and acoustically, with the proper function of a worn hearing device. Therefore, headphone and insert earphones are generally excluded from aided evaluation. Other problems associated with headphones and insert earphones include inaccuracies due to individual ear size variability and cabling interference and damage.
Portable and hand-held hearing evaluation is advantageous for conducting hearing testing outside the standard calibrated audiological setups. However, due to the relatively large errors associated with outside room acoustics, calibration, speaker-subject positioning and ambient background noise, portable and hand-held instruments tend to be limited to basic screening evaluation, requiring follow up testing in a proper audiological setup.
Review of State-of the-Art in Related Hearing Device Technology
Heller, J., in U.S. Pat. No. 4,567,881 describes a combination otoscope and audiometer for performing audiometric testing during otoscopic examination. Since the testing is performed while the tip of the otoscope is inserted in the ear canal, it is obviously not intended for aided evaluation whereby a hearing aid is worn in the ear canal. Furthermore, an otoscope is intended for use by a professional thus not suitable as a personal hearing evaluator.
Shennib, A. in U.S. Pat. No. 5,197,332 describes a headset hearing tester which is worn on the head for positioning a speaker portion directly on the ear. As previously observed, headphone type audiometry not only interferes with the proper function of most hearing aids when worn, but is also bulky and uncomfortable for many users.
Chojar in U.S. Pat. No. 5,081,441 discloses a hand-held tone generator for generating an audible tone as a test for equalizing binaural hearing aids. Chojar's device is limited to producing a single tone at single level, thus clearly not suitable for performing audiometric measurements. In fact, it is merely concerned with ensuring a balanced binaural aided hearing.
Downs, M., in U.S. Pat. No. 5,291,785 describe a hand-held portable device for testing infants for hearing defects. The device produces a low intensity sound for eliciting a response and a high intensity sound for eliciting reflex from the infant. Although designed to produce multi-level acoustic stimuli, the device is essentially a screening device for infants, thus not concerned with presenting accurate stimulus levels at multiple frequencies, nor concerned with aided evaluation. Furthermore, the device is clearly not designed for self-testing.
Posen et. al., in U.S. Pat. No. 5,732,396 disclose a hand-held screening device for generating various acoustic stimuli at a distance set by a physical spacer incorporated into the screening device. The spacer makes direct contact with the ear area for positioning the speaker at 1½ to 2¼ inches form the ear. The screening device, with a spacer incorporated within, has the advantage of providing a predetermined distance between the speaker and the test ear. However, the direct contact of the device to the ear area is not only awkward for audiometric testing, but is also difficult to operate by an individual of limited dexterity in self-testing scenarios. Furthermore, testing involving both ears simultaneously (binaural mode) is not possible with such a device.
There are numerous situations whereby it is desirable to provide a hand-held hearing evaluator with accurate multi-level test sounds. It is also desirable to provide a miniature instrument with means for self-administered testing without resorting to an expensive test performed by a hearing professional. In another situation, it is desirable to have a personal hearing evaluator to regularly verify the function of a worn hearing device. This is important since hearing aids are notorious for being subject to frequent damage and deterioration.
Therefore, it is a principal objective of the present invention to provide a hand-held hearing evaluation device for presenting multi-level and multi-frequency stimuli.
Another objective is to provide contactless means to properly position a speaker with respect to a test individual for accurate presentation of test stimuli.
A further objective is to provide a hearing evaluation device with means to automatically calibrate the level of acoustic stimuli presented.
A further objective is to provide an easy to use hand-held hearing evaluator suitable for self-administration by a test subject in either aided or unaided conditions.